Accurate sensing of angular velocity is an essential element in the guidance and control of vehicles of many types including land vehicles, manned or unmanned aircraft, guided missiles and smart munitions. Many types of partially or completely integrated optical gyroscopes have been disclosed in attempts to provide a rotation rate sensor having certain advantages over conventional rotating mass gyroscopes in terms of improved reliability and robustness, reduced size and power, and lower cost (see e.g. U.S. Pat. Nos. 4,326,803; 5,327,215; 5,408,492; 6,259,089; and 6,587,205 which are incorporated herein by reference).
Optical gyroscopes (i.e. gyros) are based on the well-known Sagnac effect which defines a linear relationship between the rotation rate of light propagating in a circuital path and a phase shift Δφ of the light propagating around the path in opposite directions given by:
      Δ    ⁢                  ⁢    ϕ    =            8      ⁢      π      ⁢                          ⁢      A      ⁢                          ⁢      Ω              λ      ⁢                          ⁢      c      where A is the area of the circuital path, Ω is the angular rotation rate, λ is the wavelength of the light, and c is the speed of light. The phase shift Δφ of the light for a given rotation rate Ω can be increased N-fold when the circuital path with the area A is looped around N times. A further increase in sensitivity of the optical gyroscope can be achieved when the circuital path forms a resonator. In this case, the phase shift Δφ will be increased by a finesse, F, of the resonator. Further details of the operation of various types of optical gyroscopes can be found in a book chapter by S. Merlo et al entitled “Fiber Gyroscope Principles” (in Handbook of Fibre Optic Sensing Technology, chapter 16, John Wiley & Sons, Ltd., 2000).
The integrated optical gyroscope of the present invention with a bidirectional laser source, phase modulators and waveguide detectors formed as a photonic integrated circuit (PIC) on a compound semiconductor substrate and with a passive ring resonator formed separately and attached thereto represents an advance in the art which is expected to provide many of the advantages listed above while being more easily fabricable using current technology than a completely-integrated device with the passive ring resonator formed on the same substrate as the PIC.
These and other advantages of the present invention will become evident to those skilled in the art.